In Goblet of Fire, Mad Eye Moody
Or rather, Barty Crouch
explained the 3 unforgivable curses to the 4th year children. He explains that Avada Kedavra needs a "good deal of magic behind it" for it to be effective and that all the students combines at their current proficiency "[wouldn't] get so much as a nosebleed".
Could a wizard/witch then not put much force behind AK and purposefully not kill someone but just harm them tremendously?